Keyless entry systems that allow a door to be unlocked without using a mechanical key are in wide use, and such a system typically comprises an electronic key carried by a vehicle operator and configured to emit a radio wave signal containing a code signal, and an onboard verification unit that authenticates the code signal received from the electronic key (see Japanese patent laid open publication no. 2002-115433).
Immobilizer systems are also in wide use. An immobilizer system typically comprises a transponder incorporated in a mechanical key and an onboard verification unit that permits the starting of the engine when a prescribed response is returned from the transponder. Thereby, an illicit attempt to steal the vehicle by using a duplicate key or the like can be prevented.
Conventionally, each vehicle was fitted with two separate control systems to control such two systems. However, as use of such systems expands, there is a growing demand to combine the two systems into a single unit which is incorporated in a single housing so that the cost for the components parts may be reduced and the manufacturing efficiency may be improved.
However, because the two systems rely on the use of radio wave for their operation, when they are combined into a single housing, it becomes necessary to prevent any interferences between the antennas for the keyless entry system and immobilizer system.